Multioffice telephone system



2 Sheets-Sheet 1 N. H. SAUNDERS ET AL MULTIQFFIGE TELEPHONE SYSTEM FiledJune 22, 1931 Feb. 28, 1933.

l Imm-IEE Nur-'marl H, Eaunclers Elr'enceE. Lmmax Thomas E Cracker Feb.28, 1933. N. H. sAUNDERs ET AL 1,899,112

MULTIOFFICE TELEPHONE SYSTEM Filed June 22, 1951 2 sheets-sheet 2 NavmanH. Saunders Clarence E. Lomax Thomas E rncker www PatentedA Feb.28,1933r UNITED STATES PATENT OFFICE NORMAN H. BAUNDEBS, OF CHICAGO,CLARENCE E. LOMAX, OF OAI PABX, ANI) TROIA! v F. CROCKEB, 0F CHICAGO,ILLINOIS, ABSIGNOBS TO ASSOCIATED ELECTRIC LABORA- TORIES, INC., OFCHICAGO, ILLINOIS, A CORPORATION 0I' DHJAWABE IULTIOFFICE TELEPHONE-SYSTEH Application med June 22,1881. Serial No. 545,933.

Thisinvention relates to multi-oilice telephone systems, particularly tomulti-oice telephone systems which include one or more unattendedautomatic oiiices, and is concerned primarily with improvedl apparatusand circuits for supervising the unattended offices.

It is the usual procedure in systems of the above type to provideswitching apparatus which, in response to an unstandard condition in anunattended office, transmits an alarm signal to an attended oilice overone of the interoilice trunk lines. In some cases the alarm signal istransmitted in the same manner as a regular trunk call, as shown in theBenson Patent No. 1,616,738 of February 8, 1927, and in other cases itis transmitted by means of special currentv sent over the trunk line.The systems disclosed in the Saunders Patent No. 1,805,726 of May 19,1931, and in the co-pending application of J. Wicks, Serial No. 395,882,filed September 8, 1929, are representative of the latter method oftransmitting alarm signals. These systems employ, respectively,pulsating current and a high voltage current for signalling, and aresuperior to the former systems in that they do not busy a trunk lineagainst regular calls when in operation.

The systems above-*referred to which are representative of thosepreviously used, are open to criticism in that they are inoperative inthe case of a total failure of the branch exchange apparatus such aswould result from the blowingr of the main battery fuse for' example.The systems are also subject to trouble from failure of the signalapparatus itself to respond properly to alarm signals. These more -orless objectionable features are overcome by the present invention, whichhas for its main object the provision of an alarm signalling systemwhich willoperate satisfactorily under any unstandard conditions whichmay arise in a branch exchange and in which a failure of the signallingapparatus itself will result in the notification of the attended oiiice.f

Another object of the invention is the provision of circuits andapparatus for relaying or repeating alarm signals through a tane4 edmanual exchange or toll switchboard asso-l ciated with a trunk lineextending to the unattended exchange shown in Fig. 1.

Referring now to Fig. 1, the various circuits shown in this figure areassumed to be .in one of the unattended oilices which will hereinafterbe referred to as oixice X. This oilice is connected with anotherunattended oiiice, which will be referred to as oiiice Z, by the trunkline TL1, and with an attended oce, which may be manually operated orwhich includes a manual switchboard, by the trunk line TL. The attendedoiiice will be referred to hereinafter as office Y. In the X oice,repeater R is inserted in the trunk line TL1 incoming from Z office andrepeats the alarm signals through oice X as a tandem center, as will beexplained hereinafter. The trunk line extending through the repeaterterminates in an incoming connector C through which access is had to thesubscribers lines in oiice X and to trunk lines extending to office Y.The trunk line TL which connects oiiices X and Y terminates in connectprC1 to which access is had to the subscribers in ofice X and to trunkline TL1 extending to oiice Z and also to a group of signal terminalsassociated with the alarm relay equipment. Connectors-C and C1 of whichonly the line and cut-off relays .havebeen shown, may be similar to theconnectors shown in the above-referred to Saunders patent. AR is a groupof alarm signal-relays which are controlled by the regular exchangealarm signalling equipment AS.

This equipment shown only in skeleton form may be of the same generaltype as that disclosed in the Saunders patent reviously referred to,andis arranged so t at the holdof the type ordinarily used forterminating two-way automatic to manual trunk lines, modified, however,to operate with the alarm signal apparatus which constitutes the presentinvention. Connection is made with this trunk line by means of a cordcircuit of the type commonly used for toll service, for

example, a. cord such as that disclosed in the Crocker Patent No.1,771,842 of July 29, 1930.

The operation of the various circuits will now be described in detail tobetter illustrate the various features of the invention. Consideringfirst the trunk line TL and its associated. apparatus, it will be notedthat relays 202 and 203 of relay group TR are normally energized. Thecircuit for relay 203 may be traced as follows: from battery through theupper winding of relay 151', contacts 153', trunk conductor 161, windingof relay 203, contacts 225 and 217,' trunk conductor 162, contacts 154.lower winding of relay 151 to ground. Relay 151 is not operated in thiscircuit due to the high resistance of relay 203. Relay 203 completes thecircuit of relay 202 at contacts 212, and relay 202 opens a point in thecircuit of relay 201 at contacts 211 to prevent the operation of thelatter relay.

A regular call from office X to Office Y will be extended to the trunkline by an incoming connector, such as C, or by a similar localconnector which has access to the trunk line. The connector on seizingthe trunk line will apply ground to release trunk conductor 158, therebyoperating cut-oit' relay 152 ot connector C1, relay 135 of the alarmrelay group AR and relay 104 of repeater R. Relay 152 disconnects linerelay 151 of connector C1 from the trunk, and relay 135 completes aholding circuit for relay 136 at contacts 166 to mark the trunk linebusy to the. alarm apparatus. Relay 104 is connected to conductor 158 byway of contacts 117 and' operates to close a circuit 4for relay C 105 atcontacts 119. Relay 105 in turn completes a circuit for relay 106 atcontacts 120 and relay 106 completes a circuit for relay 107 at contacts121. Relay 107 opens the circuit of alarm relay 108 at contacts 122,completes a new holding circuit for relay 104 at contacts 123 and opensthe signalling circuit at contacts 124. AAn alarm signal coming in overtrunk line TLl is now unable operate relay 206 which is brid ed acrosstheV trunk conductors in parallel with relay 203. Relay 206 onoperating, locks mechanically and closes a holding circuit for relay 202at contacts 218 and a circuit for lamp L at contacts 219. Lamp L glowsto notify the operator of the incoming call.

On noting the lighted condition of lamp L the operator will insert theanswering plug P of a cord circuit into jack J, thereby closing acircuit forrelay 207 at contacts 226. Relay 207 restores the armaturesof relay 206 to normal bymeans of the interlocking arm 228, disconnectsrelay 203 from across the trunk line at contacts 225, disconnects relay206 from in bridge of the trunk conductors at contacts 220, and connectsground to the lower high resistance winding of sleeve relay 205 atcontacts 222. Relay 205 operates over the sleeve of the jack and plug,extends the trunk conductors through the left-hand windings of repeatingcoil R to polarized relay 204 by closing contacts 214, connects the ringand tip springs of the jack through to the right-hand windings of therepeating coil R by closing contacts 216, and by opening contacts'215and 217, divides the trunk into two sections connected through therepeating coil. Relay 203 restores upon the opening of its circuit byrelay 207, and relay 202 restores after slight delay following therestoration of relay 206 to normal. Relay 201 is now prevented fromoperating since a second point in its circuit has been opened atcontacts 223 by the operation of relay 207'. The ring-cut-olt` relay ofthe calling connector operates in series with relay 204 and stops theapplication of ringing current to the trunk line. The operator may nowconverse with the calling subscriber and further extend the connectionby means of her cord circuit in the usual manner.v

To terminate the connection the calling subscriber will hang up and theoperator will Withdraw plug P from the jack. Connector or the connectorin use will restore, thereby removing ground from release trunkconductor 158 and relays 152', 135 and 104 to 107, inclusive, willrestore to normal. At the trunk relay group relays 205 and 207l willrestore, again bridging relay 203 across the trunk line. Relay 203 willoperate before relay 201 has time to energize since this latter relay isslow to operate. Relay 202 will operate following the operation of relay208 and will open the circuit of relay 201 at -with t e same results aspreviously-described,

except that relay. 206, not having operated, is not restored to normal.The line rela of connector C1 is now o erated over a oop' Each time thecalling device is turned oil'- normal the circuit to sleeve rela ,205 isopened and that relay restores -an extends the trunk conductors straightthrough to the ring and tip conductors of the j ack 'and plug by way ofcontacts 215l and 217. Upon the call being answered, the connection ofline relay 151 to the trunk conductors is reversed by means of the usualreversing contacts on the vbattery-feed relay ofconnector C1, andpolarized relay 204 of the relay group TR operates. Ground is connectedthrough the low-resistance upper winding of relay 205 by way of contacts213 to operate the super visory signal in the cord circuit in the wellknown manner. Upon the termination of a call the called subscriber willhang-upand i the operator will withdraw the plug from the jack J,thereby releasing the apparatus in the manner previously described.

A call from office Z to oiiice X or Y 'will' be extended over the trunkline TL1 by a connector similar to connector C in the Z oilice. Theseconnectors, it will be appreciated, are arranged to switch through andoperate as selectors on certain levels, in which case no ringing currentis transmitted over the called trunk line and dialled impulses are`repeated to operate succeeding switches. Upon the seizure of the trunkline TL1 a loop circuit will be closed for line relay 152 of connectorC. This loop includes the upper and lower winding of differential relay101 which does not operate under these conditions since its two windingsoppose each other. Relay 152 on operating, prepares connector C foroperating and the connector in the usual way returns a holding ground onrelease trunk conductor 157.

This ground by way of contacts 111 operates relay 102 whichshort-circuits the two windings of relay 101 andl at contacts 113 and114, and opens a point in the circuit of re lay 103 at contacts 112. Thecalling sub- 204 does not oper-l scriber now dials the number of .thewanted subscriber and connector C operates in the usual way to extend aconnection. Itis further noted that connector C also has access lto thetrunk line TL and b dialing the proper number the callin su criber isable to call the operator at t e oilice Y in lieu of a subscriber in theX otlice.

A'call from oice X or oice Y to oilice Z will be extended over the trunkline TL1by an incoming connector such as C1 or a simllar localconnector. The connectors of this type on seizing the trunk line inquestion switch throu h and operate as selectors and repeat the dialledimpulses over the trunk line. U on seizing the trunk line, ground isextende ahead upon release conductor 157, operating relay 102 of the reeater R which short-circuits the windings o differential relay 101 andopens the circuit to relay 103 as previously described. The setting u ofthe connection and release thereof fol ow the usual well-known routineoperations and will not be described in detail.

The normal operation of the trunking apparatus has now been consideredand the operations involved in the transmission of alarm signals willnow be described. Referring to the alarm relay group AR, Fig. 1, it willbe noted that relays 131 and 134 are normaly ener ized by batteryconnected to the alarm con uctors 163 and 164, respectively. Relay 136is held operated over a circuit including contacts 139 and 143. Relay131 disconnects the upper winding of relay 132 from test conductor 165at contacts 140 and relay v 134 disconnects the lower winding of relay133 from this same conductor at contacts 144. Relay 136 maintains thealarmv circuit open at contacts 145, opens the circuit of relay 137 atcontacts 146 and connects relay 135 to release trunk conductor 158 atcontacts 147. In the case of an emer ency alarm, the alarm signalapparatus A operates in the usual manner and battery is disconnectedfrom conductor 163, thereby permitting relay 134 to restore. In the caseof a regular alarm the battery is disconnected from conductor 164,thereby permitting relay 131.to restore. The release of either of theserelays opens a point in the circuit of relay 136 at either contact 139or Contact 143 and the associated cut-off relay 132 or134 is connectedto conductor 165. In the event that the trunk line TL is in use at thetime the alarm signal comes in, relay 135 will be operated as previouslydescribed and relay 136 will be prevented from restoring since a holdingcircuit is closed by way of contacts 166. In case the trunk line TL isidle or, when it becomes idle after having been in use, relay 135 willrestore upon the removal of ground from release trunk conductor 158 andthe circuit of relay 136 will be opened, thereby permitting that relayto restore. Relay 136 on restoring disconnects relay 135 from therelease trunk conductor at contact 147, closes a circuit for relay 137at contacts 146, and at contacts 145 connects ground to the upperconductor of the trunk line TL over a circuit extending by way ofcontacts 149, resistance 150, and conductor 159 to conductor 161. Thisground operates relay 151, althou h no useful purpose is served thereby.elay 203 of the trunk group TR is normally operated in series with relay151', as previously explained, and upon the connection of ground toconductor 161, the relay is shunted and restores. The circuit of relay202 is opened at contacts 212 and after a short delay relay 202 restoresand closes the circuit of relay 201 at contacts 211. Relay 201, after ashort delay, operates and completes a locking circuit for itself by waof contacts 210 and contacts 227 of key The alarm circuit is closed atcontacts 209 and the bell and lamp L2 are operated to notify theattendant atthe main exchan e that an unstandard condition has developeat the unattended exchange. Returning now to the alarm relay group AR itwill be recalled that the circuit of relay 137 was closed upon therelease of relay 136. Relay 137 is provided with a Weighted springarmature which is set in vibration upon the operation of the relay. Thevibrations of the armature spring gradually decrease and contacts 148remain closed for a longer interval as the relay is maintainedenergized. After a delay which is governed by the adjustment of theweight on the armature springs, contacts 148 remain closed long enoughfor the high-impedance relay 138 to operate. This relay opens the signalcircuit at contacts 149, thereby removing the shunt from relay 203 andrestorin the trunk line to normal condition. Rela 136, however, willremain in normal condltion as long as the unstandard condition ersistsor until the operator at the attende exchange calls back to verify thealarm as will be explained later, and relays 137 and 138 will alsoremain operated. Relay 201 at the main exchange will remain locked upand the alarm signal will be operated until released by the operation ofkey K which opens the holding circuit of relay 201 at contacts 227. Thetrunk line TL will be available for regular calls immediately afterrelay 138 is operated.

In order to determine the Character of the unstandard condition of thebranch exchange, the operator will call back over trunk line TL or asimilar trunk line, operating the associated connector, such as C1, intoengagement with the set of contacts including test contact 160. Upon theconnector engaging this set of contacts, ground over the test wiper ofthe connector by way of conductor 165 and either of the closed contacts140 or 144, will operate the particular cut-0E relay which has beenconnected to conductor 165.

Laaeana Assuming that rela 132 is the' relay involved, t is relay w' llock in series with relay 131 by way of contacts 141 and therebyoperating that relay and again closing the cli-cuit for relay 136 atcontacts 139. Relays 131 and 132 will remain locked up and prevent thealarm from being retransmitted to the main exchange. When the unstandardcondition is remedied the connection of batter to conductor 164 willshunt relay 132 anni1 will maintain relay 131 operated in the usual way.The restoration of relay 132 will place the apparatus in condition forits usual operation. The operation of relay 133 is substantially thesame as that of relay 132, except that its up er winding is locked inseries with relay 134 by way of contacts 142. The alarm signal apparatusAS applies various tones to the contacts engaged y the wipers of thecalling connector to inform the operator of the character of theunstandard condition. This arrangement is shown in detail in theSaunders patent referred to in the early part of the specification andneed not be described in detail at this point.

In the case of an unstandard condition in the unattended oiice Z, analarm signal relay apparatus similar to AR will be operated, therebyapplying ground to conductor 128 of the trunk line TLl. Application ofground energizes the upper winding of relay 101 in series with the upperWinding of relay 152 of connector C. Relay 101 upon operatlng, completesa circuit by way of contacts 110 and 112 to slow-to-operate relay 103.Relay 103 upon operating, completes a locking circuit for itself atcontacts 115, closes a circuit for relay 108 at contacts 116,

g opens the circuit of cut-off relay 104 at cony tacts 117, and atcontacts 118 applies ground by Way of contacts 124 and 127, resistance130 and conductor 159 to trunk conductor 161 of the trunk line TL.Relays 203 and 202 of the trunk relay group TR, Fig. 2, restore as inthe previous case, relay 201 operates and locks and completes a circuitfor the alarm bell and lamp. Relay 108 of repeater R is provided with aweighted armature spring, similar to that of relay 137, and after adelay determined by the adjustment of the Weight on this armaturespring, a circuit is completed for relay 109 at contacts 125. Relay 109which has a high impedance operates after a slight delay, opens thealarm signalling circuit at contacts 127 and opens the locking circuitof relay 103 at contacts 126. The ground is removed from the trunkconductor 128 of trunk line TLl after a short interval by a relaycorresponding to relay 138 of the relay group AR at the office Z. Relay101 consequently restores to normal and upon the operation of relay 109relay 103 restores to normal and opens the circuit of relay 108. Relay108 in turn restores and opens the circuit of relay 109 and the reter isreturned to normal condition and 1s available for ar calls.

In the case of a ailureof the alarm signal apparatus itself, such as theblowin of a 5 fuse in the battery-feed circuit, relay 1 6 will restoreand apply ground to trunk conductor 161 to operate the alarm signal inthe attended exchange In this case, however, relays 137 and 138 will notoperate to free the trunk line for regular calls. The attendant will beapprised of this condition by continued operation of the alarm signalafter the opera- .tion of the alarm release key K.

Should a fault develo on the trunk line TL, for example, the brea lng ofeither trunk conductor or the grounding of conductor 161, the alarmsignal at the attended exchange will be operated. In-either case, relay203 will be released to initiate the si al o eration. The attendant willbe apprised o this condition in the manner described above, that is, thesignal will persist even though the alarm release ke K is operated.

It will be note that the alarm signals from both oiiice X and oice Z aretransmitted over trunk line TLl to the main exchange oiiice Y. Thisarrangement has been shown for convenience only, and it is obvious thatthe repeater R may be arranged to transmit alarm signals overa differenttrunk line from `that used by the apparatus AR when such is desired. Itis also evident that in the transmission of alarm signals theinter-oilice trunks are withheld from` regular service for the veryshort interval required to operate the relays 137 and 138 or the relays108 and 109 and that after the alarm signal has been transmitted to themain exchange, the trunk line is again restored to normal use.

What is claimed is: fr 4 1. In a telephone system, two exchanges, atrunk line connecting said exchanges, a signal device at one exchange,means at the other exchange automaticall operated res onsive to anunstandard con ition therein or momentarily connecting ground to aconductor of said trunk line to initiate the continuous operation ofsaid signal device.

2. In a telephone system, two exchanges, a trunk line connecting saidexchanges, a signal device at one exchange, means at the other exchangevoperated responsive to an unstandard condition therein for momentarilyconnecting ground to a conductor of said trunk line to operate saidsignal device, means at said one exchange for maintaining the operatedstate of said signal device after the ground connection to the trunkconductor is removed, and manually controlled means at said one exchangefor disabling said last means. l

3. In a telephone system, two exchanges, a trunk line connecting saidexchanges, means for establishing talking connections between 05subscribers in said exchanges over said trunk 1n e other exchangeoperated responsive to an unstandard condition therein `'for momentarilyconnecting thetrunk line, an means at the other exchange operatedresponsive to said ground connection for initiating the continuousoperation of said signal device.

l 4. In a telephone system, two-exchanges, a trunk line connecting saidexchanges,a signal at one exchange, and means associated with said trunkline at said one exchange for op. erating said si nal responsive to anunstandard conditlon either in said other exchange or on said trunkline.

5. In a telephone system, two exchanges, a trunk line connecting saidexchanges, a signal at one exchange, means associated with the trunkline at said one exchange for actuating said signal responsive to anunstandard condition either in the other exchange or on the trunk line,and manually controlled means at said one exchange for deactuatin saidsignal when the same has been actua responsive to an unstandardcondition in said other exchange.

6. In a telephone system, two exchanges, a trunk line connecting saidexchanges, means for establishing talking connections betweensubscribers in said exchanges over said trunk line, a signal .in oneexchange, means in said one exchange controlled over said trunk line andoperated responsive to an unstandard condition either in the otherexchange or on the trunk line for initiating the continuous operation ofsaid signal, and manuall controlled means at said one exchange e ectivefor disabling said signal only in case the signal has been operatedresponsive to an unstandard condition in the other exchange.

7 In a telephone system, two exchanges, a two conductor trunk lineconnecting said exchanges, switching apparatus in said exchanges, meansfor establishing talking connections between subscribers linesterminating in said exchanges via said trunk line and said switchingapparatus, a signal device at one exchange, a signal at the otherexchange, means including said device operated responsive to thedevelopment of a fault in the switching apparatus at said4 one exchangeound to a conductor of linetaa signal device. in oneexchan'ge, means.los

for momentarily connecting ground to one conductor of the trunk line,and means at the other exchange controlled by said mo'- mentary groundconnection for initiating the continuous operation of said signal.

8.'In a telephone system, twoy exchanges, switching apparatus andsignalling apparatus in one exchange, an 'alarm signal in the otherexchange, a trunk line connecting said exchanges, means for establishingtalking connections between subscribers 1n sald exchanges lover saidtrunk line and through said switching apparatus, means including saidsignalling apparatus for momentarily connecting ground 4to a conductorof said trunk line to operate said alarm signal responsive to anunstandard condition in said switching apparatus, and means forcontlnuously connecting ground to sald conductor to operate said signalrespons1ve to an unstandard condition in said signalling 'currentbridged across the trunk conductors at the other exchange formaintaining said relay in operated condition, and means at said otherexchange for shunting said current source to release said relay andoperate said si al. v

11. n a telephone system, two exchanges a two conductor trunk lineconnecting said exchanges, means for establishing Vtalking connectlonsbetween subscribers in said exchanges over said trunkline, a signal atone exchange, a relay for .controlling said signal, a second relaynormally Venergized over the trunk line from a source of current in theother exchange for preventing the operation of said first relay,andmeans for releasing said second relay while still preventing theoperation of said first rela responsive to the establishment of a taling connection over the trunk line.

12. In a telephone system, an attended exchange, a plurality ofunattended exchanges, trunk lines serially connectin said exchanges, asignal in the attende exchange, and means operated responsive to anunstandard condition in one of said unattended exchanges for momentarilyconnecting ground to a conductor of each of the intervening trunk linesto initiate the continuous operation of said signal.

13. In a telephone system, an attended exchange, a plurality ofunattended exchanges, trunk lines serially connectin said exchanges, asignal in the attende exchange, means for establishing talkingconnections between subscribers in different ones of said exchanges overone or more of said trunk lines, means operated responsiveto anunstandard condition in one of said unattended exchanges for initiatingthe continuous operation of said signal by the momentary connection ofground to the intervening trunk lines, and means whereby theestablishment of talking connections over said trunk lines is preventedonly during the interval through whicel said ground connections aremaintain 14. In a telephone system, three exchanges, trunk linesserially connectin 'said exchanges, a signal at the thir exchange, meansfor establishing talking connections between subscribers in di'ercntexchanges over said trunk lines,-n1eans in the first exchange operatedresponsive to an unstandard condltlon therein for momentarily connectlngground to the trunk line extending to the second exch-ange rovided' thetrunk line is notan use in a tal ing connection, means in the secondexchange controlled by said signal current for momentarily connectingground tothe trunk line extending to the third exchange to operate saidsignal provided the trunk line is not in use in a talking connection,and means in the second exchange operated when the trunk line extendingto -thethird exchange is in use in a talkingconnection for causing saidlast means to withhold the ground conneetionfromthe trunk line until thesame is released from the talk ing connection. l

15. In a telephone system, three exchanges,

a two `conductor trunk line connecting the first and second exchanges, atwo-iconductor v trunk .connectingfthe 1second ..and third'exchanges,means for est ablishing talking `coni nections between subscribers indifferent. ex-4 changes over said trunk lines, means resp0nsive to an'unstandardf condition in the firstV connectingL exchange formomentarily ground to a conductor of said first trunk line, means in thesecond exchange controlled by said ground connection for momentarilyconnectin ground to `a'conductor of said second trunki n set in aVcontinuously operated condition responsive to said. last groundconnection..

16. The method of supervising an unattended tclephone exchange over atwo conductor trunk line ordinarily` used for establishing talkingconnections to and from subscribers lines, which consists in disablingan alarm signal b energizing a relay over the two trunk condilctors inseries as long as the exchange apparatus and the trunk line remain inoperating condition and the trunk line remains idle. Y

17. The method of supervising an unattended telephone exchange'overa'two conductor trunk line ordinarily used for establishing talkingconnections to and from subscribers lines, consisting of disabling analarm signal by energizing a relay over the two trunk conductor inseries as long as the exchange apparatus and the trunk line remain inoperating condition and the trunk ne, and a signal in theA thirdexchange v Yllt) our names this 17th da scribers lines, consisting ofnormally energizing a relay over the trunkv line and of automaticallyconnecting ground to the trunk line to deenergize the rela when anunstandard condition develops m the exchange.

19. The method of automatically transmitting alarm signals from oneexchange to another over trunk lines ordinarily used for establishingtalking connections between sub scribers in the different exchangesconsisting of appl ing. ground to a trunk conductor at one exc ange toshunt a signal control relay at the other exchange which is normallyheld energized by current flow over the trunk line from a current sourcein the one exchange.

In witness whereof, we hereunto subscribe of J une A. D. 1931. NORMA H.SANDERS. f CLARENCE E. LOMAX. THOMAS F. CROCKER.

